By Robert Paxton, Updated March 24, 2022
Polystyrene and polyurethane are two widely used synthetic polymers, each with distinct properties that make them suitable for different applications. While polystyrene has long been a staple in items such as computer housings and disposable containers, polyurethane is increasingly chosen for projects that demand flexibility, durability, and superior performance under stress.
Polystyrene is a homopolymer made from styrene monomers, producing chains composed mainly of carbon and hydrogen atoms. In contrast, polyurethane is a segmented copolymer that incorporates carbon, hydrogen, nitrogen, and oxygen. This chemical diversity allows polyurethane’s chains to be engineered for a wide range of flexibilities—from rigid boards to elastomeric foams.
In building and insulation contexts, the R‑value measures how well a material resists heat flow. Polyurethane typically offers an R‑value roughly twice that of polystyrene, making it a superior insulator. Importantly, polyurethane retains its flexibility even in cold climates, only beginning to stiffen gradually around 0 °F. Polystyrene, while effective at moderate temperatures, tends to lose structural integrity when exposed to low temperatures.
Polyurethane does not melt under heat; it remains largely intact until temperatures reach about 700 °F, where it begins to char. Polystyrene, on the other hand, melts in the 200–300 °F range, releasing flammable fumes. Consequently, polyurethane is the preferred choice for applications where fire safety is critical.
Polyurethane exhibits broad chemical resistance, tolerating solvents such as gasoline, many insecticides, and industrial cleaners. It also resists UV degradation and oxidation better than polystyrene, which can become brittle when exposed to solvents or prolonged sunlight. In terms of mechanical wear, polyurethane’s elastomeric nature allows it to absorb impacts and stresses more effectively than the hard, brittle polystyrene.
Because of its hybrid plastic‑rubber character, polyurethane is ideal for load‑bearing components such as wheels, mechanical joints, couplings, and machine mounts. Its ability to absorb shock and distribute forces makes it far superior to polystyrene for these high‑stress roles.
Polyurethane’s rubber‑like damping properties make it an excellent material for noise abatement. Gears and other moving parts fabricated from polyurethane operate more quietly than their polystyrene counterparts, reducing mechanical vibration and sound.
Choosing between polystyrene and polyurethane depends on the specific performance criteria of your project. For rigidity and cost‑effectiveness, polystyrene may suffice; for flexibility, fire safety, chemical resistance, and load‑bearing capacity, polyurethane offers a clear advantage.
